1. Field of the Invention
This invention relates generally to a magnetic recording medium having a magnetic coating or layer on a non-magnetic base, for example, as in magnetic recording tape.
2. Description of the Prior Art
When a magnetic recording tape is used in a tape recorder, the speed at which the tape is driven relative to the magnetic head of the tape recorder is very high, for example, 19 to 38 cm/sec. Since the magnetic tape engages or contacts tape guide members and the like during its high speed movement, the useful life of the tape is inevitably shortened by the resulting abrasion. Further, due to the fact that existing magnetic tape is insufficiently lubricated, the magnetic head is severely abraded or worn by the contact of the tape therewith. Although many efforts have been made to improve the lubrication and wear-resistance of magnetic tape, magnetic tape that is sufficient in these characteristics has not been achieved heretofore.
In the prior art, graphite, molybdenum disulfide, castor oil, olive oil and the like have been used as lubricants for magnetic tape, but these substances do not afford long-lasting lubrication to the magnetic tape. It is also known that a certain silicon derivative has a desirable lubricating effect, but such silicon derivative has a so-called blooming phenomenon in which the surface of a magnetic layer containing the silicon derivative becomes rough and uneven and the magnetic powder sticks to and clogs the magnetic head and thereby deleteriously affects its sensitivity.
Further, it has been proposed, for example, in U.S. Pat. No. 3,492,235, issued Jan. 27, 1970, and having a common assignee herewith, to employ, as lubricants for magnetic tape, ester lubricants produced by reaction between a pure monobasic fatty acid or a mixture of two or more monobasic fatty acids containing from 2 to about 18 carbon atoms, and a monohydroxy aliphatic alcohol containing more than 14 carbon atoms. Such ester lubricants include stearyl butyrate, stearyl stearate and stearyl laurate, and are preferably used in combination with high molecular weight hydrocarbon lubricants, such as squalene, squalane, pristane and eicosane. However, the above ester lubricants, particularly when used alone in sufficient quantity to provide a suitably reduced coefficient of friction for the magnetic recording tape or other medium, also produce the undesirable blooming phenomenon and resulting head clogging.